1. Field of the Invention
This invention relates to battery protection circuitry, and more particularly to a method and apparatus of preventing early shutdown of computer systems due to a power demand change.
2. Background Information
Computer systems that are capable to be powered by battery or a direct current (DC) source that is supplied through an alternating current (AC) adapter typically have mechanisms to protect batteries from damage and to allow the system to switch between the two types of power sources. The main purpose of these battery protection circuits are to detect: whether the battery has enough energy to run the system, i.e. the battery is good, the battery is low, or the battery is critically low. This information is used by the system power management controller to determine if a power failure is about to occur, or to shutdown the whole system itself. This is done to prevent deep charging of the battery which can cause irreversible damage to the battery.
Many computer systems that are powered by either battery or DC sources through an AC adapter, such as notebook computer systems, have different processing speeds depending on the power source. Some of these notebook computer systems will run at a higher processing frequency when powered by an DC supply through an AC adapter as opposed to battery power. When the power source switches between the DC source and battery, a transient may occur. This transient can lead to a false reading by the power management system, thus causing the computer system to prematurely shutdown. As the batteries in computer systems become smaller, i.e. less battery cells, (which reduces the weight and can also reduce the size of the system) the transient becomes greater and the reliability of the power management system becomes a greater issue.